Reining in Roaring

It’s a big day at the track. Years of training and thousands of dollars are at
stake. The gates open and your horse lunges forward. But his breath comes
in gasps. It looks as if he’s wearing a heavy mask that is blocking his access to
air. Worn nerves signal sluggishly to weakened muscles that barely respond
enough to open his airway. He slows and falls to the back of the pack.

This career-limiting problem affects nearly 8 percent of race horses and a higher percentage of sport horses. Oficially called “recurrent laryngeal neuropathy,” the common equine disease is better known as “roaring” for the strained sounds affected horses make when they try to run. It shares similarities with human vocal cord paralysis, a neurological condition
causing difi culty breathing and loss of speech and requiring tracheostomy and intensive surgery. Roaring starts early and
unseen, slowly wearing down the nerves that stimulate the muscle responsible for opening the larynx.

“Upper airway problems cause poor performance in many race horses,” said Dr. Jonathan Cheetham, an equine surgeon and sports medicine practitioner at Cornell’s Equine Hospital. “Symptoms often show in a horse’s second to fourth year, when a trainer has already invested thousands in its athletic career. The standard treatment, surgery called a laryngeal tie-back together with a ‘lazer hobday’ procedure to remove the vocal cords, returns 65-70 percent of treated horses to racing. But that’s after six weeks of recovery and another six weeks to regain fitness. It takes a toll on the horses, their trainers, and the racing economy.”

Taking roaring by the reigns, Dr. Cheetham and the Equine Performance Clinic team are helping to change how veterinarians look at and treat the disease. The team running the Clinic’s indoor treadmill offers good client service while researching new methods to diagnose disease earlier and improve treatments.

According to Cheetham, the horse is a useful preclinical model of human airway disease. Much of what he is learning and working out at Cornell could help restore function in human patients with laryngeal disease. The Equine Performance Clinic pioneered techniques using a trans-esophageal ultrasound to evaluate airway muscles in horses. Developed at Cornell with support from the Harry M. Zweig Memorial Fund, these techniques could give human doctors a new view of deteriorating laryngeal muscles and let them follow progress after treatment.

The team is developing a novel treatment for roaring using a laryngeal pacemaker to electronically stimulate the muscle and maintain its function: another technology applicable to humans with vocal paralysis.

Cheetham has spent the past year developing new ways of detecting neurological disease earlier, thanks to a grant from the Grayson Jockey-Club Foundation.

“Motor nerves need insulation from myelin sheathes to carry signals quickly,” said Dr. Cheetham. “Laryngeal neuropathy works by breaking down myelin in the two major meter-long nerves controlling the horse’s airway muscles, slowing their conduction velocity and cutting off the muscles from adequate stimulation. If we can use nerve conduction velocity to detect early myelin breakdown we may be able to catch the disease before the muscle starts shrinking.”

Placing tiny needles into the nerves, Dr. Cheetham measured conduction speeds across their length to see how speeds vary across the nerves. Next he will validate a technique that does not use needles and look at how nerve conduction velocity at the weanling stage affects performance of 2-year-old horses with the hope of confirming it as a viable diagnostic and predictive tool. Validating such a test would expand the window of detection and open doors to earlier prevention and treatments, and aid understanding of the disease mechanisms that produce ‘roaring’ in horses.

“We have also been developing ways of enhancing nerve grafting using tissue engineering techniques,” said Dr. Cheetham. “If we can pick up problems early, we might be able to treat without invasive surgery or a permanent implant. It could be safer, cheaper, and faster, and may improve the success of recovery from airway diseases in both horses and humans.”